‘There is a perception that single-celled organisms are asocial, but that is misguided. When bacteria are under stress—which is the story of their lives—they team up and form this collective called a biofilm. If you look at naturally occurring biofilms, they have very complicated architecture. They are like cities with channels for nutrients to go in and waste to go out.’----------Andre Levchenko, PhD, Johns Hopkins University
Probably the last thing one thinks of when hearing about microorganisms is their social life. Who knew they even had one? But, recent research has uncovered the complex, discriminating, and sophisticated social life of microbes.
Evidence of the gregarious behavior of bacteria has been noted in the form of biofilms. Biofilms are somewhat analogous to multicellular organisms in coordination and cooperation. They represent closely adherent communities of microbial cells, sessile in their growth mode, and found on inert or living surfaces, entrenched in a sticky matrix of DNA and other secreted polymers. In fact, the secreted polymeric substance composed of sugars, proteins, and DNA is the hallmark of bacterial biofilms.
Biofilms may contain a single species or multiple species of bacteria; the prevalence of biofilms suggests that this communal living is important for maintenance of microbial diversity and interaction with the environment. Moreover, biofilms are remarkably less sensitive to antibiotics than planktonic or free-living microbes and present human health threats, such as acute and chronic infections including periodontitis and dental plaque, degradation of medical implants, and contamination of drinking water mains.
Bacterial biofilms are physiologically different from their planktonic counterparts resulting, at least in part, from altered gene expression. In addition to being resistant to antibiotics, bacteria in biofilms can be difficult to culture. Biofilm bacteria cause most ear infections (otitis media). For example, the bacterial pathogen Streptococcus pneumoniae can form biofilms, particularly in the middle ear of children who have repeated bouts of otitis media. The biofilm formation may explain why some ear infections are difficult to treat and resistant to many antibiotics.
Bacteria in biofilms coordinate their gene expression and communicate decisions through quorum sensing. A variety of different chemicals or molecules are used as signals or inducers, which build to activation level as the population grows or a quorum is reached. Quorum sensing and environmental conditions appear to be interdependent in the impact on biofilm formation.
Why is a biofilm produced? What advantages does it confer? A few years ago, Kimberly Jefferson (2004) proposed possible advantages: protection, more effective use of nutrient resources, and other cooperative benefits of community living. Jefferson suggested that perhaps biofilms are the natural mode of growth, and the laboratory version is the aberration.
This year, researchers at the Institut Pasteur and the French National Scientific Research Centre (CNRS) showed for the first time that certain viruses are capable of forming biofilm-like collectives, resembling those formed by bacteria. The scientists have suggested that the extracellular assemblies as demonstrated with the human T-cell leukemia virus type 1(HTLV-1virus) may protect the viruses from the immune system and enable greater infectious transmission from cell to cell.
There is much to be learned about the sociobiology of microbes, and hopefully, understanding the behavior will lead to better treatments and strategies to mitigate disease.
References and Read-more-about-it:
1. Marshall Protocol Knowledge Base, Autoimmunity Research Foundation. Biofilm Bacteria. Available at: mpkb.org/home/pathogenesis/microbiota/biofilm. Accessed June 10, 2010.
2. CNRS (Délégation Paris Michel-Ange) (2010, February 8). Biofilms: Discovery of a new mechanism of virus propagation. ScienceDaily.
3. Ana-Monica Pais-Correia, Martin Sachse, Stéphanie Guadagnini, Valentina Robbiati, Rémi Lasserre, Antoine Gessain, Olivier Gout, Andrés Alcover & Maria-Isabel Thoulouze. Biofilm-like extracellular viral assemblies mediate HTLV-1 cell-to-cell transmission at virological synapses. Nature Medicine, 2010; 16 (1): 83 DOI: 10.1038/nm.2065.
4. Jefferson KK. What drives bacteria to produce a biofilm? FEMS Microbiol Lett. 2004 Jul 15;236(2):163-73.
5. Landini P, Antoniani D, Burgess JG, Nijland R. Molecular mechanisms of compounds affecting bacterial biofilm formation and dispersal. Appl Microbiol Biotechnol. 2010 Apr;86(3):813-23. Epub 2010 Feb 18.
6. Nadell CD, Xavier JB, Foster KR. The sociobiology of biofilms. FEMS Microbiol Rev. 2009 Jan;33(1):206-24. Epub 2008 Dec 3.
7. Allegrucci M, Hu FZ, Shen K, Hayes J, Ehrlich GD, Post JC, Sauer K. Phenotypic characterization of Streptococcus pneumoniae biofilm development. J Bacteriol. 2006 Apr;188(7):2325-35.